Generally, the current tire pressure monitoring sensors directly sense air pressure by using a pressure measuring aperture (air aperture), so as to measure the pressure. The air aperture is required not to be blocked. Once it is blocked, the change in pressure cannot be sensed correctly, and the deviation of the measurement is relatively large.
However, in the engineering vehicles or some special vehicles, due to their special environments, liquid is usually added into the tire, and there are much dust and other impurities in the working environment. Thus, for a tire pressure sensor using the air aperture, the air aperture can be easily blocked by the liquid in the tire. As such, it is difficult to accurately measure the tire pressure.
FIG. 1 is a sectional view of a chip package 50 of a prior art tire pressure monitoring sensor. The main problems with the prior art include the following issues.
1. The pressure input aperture is very small and can be easily blocked, and once blocked, the pressure cannot be sensed. Thus, it is impossible to detect the pressure and output a signal.
2. Since the front side of the sensor chip 52 is in direct contact with the measured environment and the bonding wire (gold wire) 54 and other materials 56 are also in direct contact with the measured environment, the reliability and the compatibility of the product are greatly influenced.
3. In the engineering vehicles or some special vehicles, due to their special environments, liquid is usually added into the tire, and there is much dust and other impurities in the work environment, which increases the risk of blocking the air aperture and damaging the chip 52 and bonding wire 54.
In view of the above problems, German patent No. DE 102010000003 discloses a pressure sensor available for measurement in an environment in the presence of liquid, which uses a permeable protective film for sealing. In practical use, it is necessary to consider the permeability of the protective film. If the pressure sensor is applied to the measurement of tire pressure, after long-term operation, dust and impurities are easily deposited on the surface of the protective film, thereby making the sensor ineffective and resulting in inaccurate measurement and other abnormal situations.
Chinese patent No. CN 00226918.X discloses a pressure sensor suitable for use in a liquid environment, which senses the pressure by using a thin metallic diaphragm. However, since the metallic diaphragm is very thin, it is easily deformed under the action of an external force, resulting in inaccurate pressure measurement. Thus, the pressure sensor is unsuitable for operation in a tire environment in the presence of liquid and impurities.